1. Field of the Invention
The present invention relates to a monolayer metal gasket adapted disposed between the mating surfaces of, for example, a cylinder block and cylinder head, and composed of a core plate surrounding bore apertures and a perimetral member extending throughout the entire perimeter of the core plate.
2. Description of the Prior Art
Conventionally, there has been well known a monolayer metal gasket disclosed in Japanese Patent Laid-Open No. 44847/1993, which is of an elastic metal member provided thereon with beads extending around cylinder bore apertures and made reduced in thickness by etching, with the exception of perimetric edges defining the cylinder bore apertures.
Japanese Utility Model Laid-Open No. 88769/1992 discloses a metallic head gasket making it possible to control the sealing around the bore apertures and the sealing about other perforations independently of each other. The bore apertures are kept sealed with metallic plates having beads extending around the bore apertures, whereas other perforations are sealed with metallic thin plates made with half beads formed about the perforations.
Also, a monolayer head gasket has been well known, which is adapted to use for an open-deck type engine having a cylinder block provided therein with water jackets surrounding continually the cylinder bores. The monolayer head gasket is disclosed in, for example, Japanese Patent Laid-Open Nos. 233105/1996 and 285080/1996, where the head gasket consists of a metal plate great in thickness for sealing around cylinder bores at areas inside the water jackets and another metal plate thin in thickness for sealing around the cylinder bores at areas outside the water jackets, the metal plates unlike in thickness being jointed together by lap welding.
Any prior head gasket enumerated above, as shown in FIG. 13, is comprised of a core plate 2P surrounding bore apertures 3P and a perimetral member 1P extending throughout the entire perimeter 6P of the core plate 2P. Moreover, the core plate 2P is provided thereon with beads 7P extending around the bore apertures 3P and has a radial width uniform throughout circumferentially of the bore apertures 3P. Thus, none of the prior head gaskets realizes the technical concept of compensating for the sealing stress occurring around the bore apertures. What no prior core plate 2P, as explained just above, varies continually in width along the bore apertures apparently results in failure, under some tightening conditions, in making the sealing stress uniform throughout around the bore apertures, especially, in compensating for the sealing stress at areas neighboring tightening holes 5P.
The conventional head gaskets constructed as described above have a disadvantage of the reduced freedom of gasket design, flexibility and adaptability when employed in many kinds of engines, which are diverse in tightening conditions of bolts to join the cylinder head to the cylinder block. In some tightening conditions to mount the cylinder head on the cylinder block, the prior head gaskets have been too tough to ensure the uniformity of the sealing stress around the bore apertures 3P, especially, at the areas neighboring the tightening holes 5P.
In closed-deck type engines having the water jackets provided in an intermittent manner around the cylinder bores, on the other hand, the cylinder block is mostly great in rigidity or stiffness, compared with the open-deck type engines, and therefore has the tendency to somewhat higher tightening or hold-down load, compared with that in the open-deck type engine. This, in some design requirements of engine, causes the sealing stress around the bore apertures a local rise at the areas nearby the tightening holes, thus making it tough to ensure the sealing stress that is uniform throughout around the bore aperture. In order to cope with the drawback in the sealing stress around the bore aperture, the metal gasket is required to have means for balancing minutely the sealing stress throughout around the bore aperture.
In the monolayer metal gasket comprised, as described above, of the thick core plate surrounding the bore apertures and a perimetral member extending throughout the entire perimeter of the core plate, the core plate uniform in radial width throughout around the bore apertures experiences the sealing stress distribution such that the stress, though becoming high at areas neighboring the tightening holes, lowers at other areas remote from the tightening holes.
The head gaskets for latest engines requiring low rigidity or/and high combustion pressure frequently involve a major problem to be solved, in which minute variations in the sealing stress occurring circumferentially around the bore apertures has an influence undesirable from the view point of sealing performance of the metal gasket.
The present invention has as its primary object to overcome the problem described just above and, especially, the provision of a monolayer metal gasket that may be preferably used in a closed-deck type engine, in which the tightening load is preselected at a somewhat high level. More particularly, the present invention provides a monolayer metal gasket simple in construction, in which a thick core plate surrounding bore apertures varies continually in radial width circumferentially of the bore apertures to compensate for minute variations in sealing stress around the bore apertures, thereby ensuring the uniformity of the sealing stress throughout around the bore apertures.
The present invention is concerned with a monolayer metal gasket adapted to be used disposed between mating surfaces of a cylinder block and cylinder head held together with tightening bolts, which comprises a core plate formed in combination of areas surrounding bore apertures and provided thereon with beads extending around the bore apertures and bridges connecting in series any adjacent two of the areas to one another, and a perimetral member extending throughout around the core plate and joining with a perimetric edge of the core plate, the core plate being made greater in thickness than the perimetral member; the improvement wherein the areas of the core plate surrounding the bore apertures are made varied continually in radial width, depending on a sealing stress distribution around the bore apertures, whereby the variation in radial width of the core plate circumferentially of any bore apertures results in compensating partly for the sealing stress distribution around the bore apertures.
In accordance with an aspect of the present invention, a monolayer metal gasket is disclosed, wherein the bridges in the core plate have any width extending across an area between any adjoining bore apertures, which width may be made either equal to or different from each other at every area between the adjoining bore apertures.
In another aspect of the present invention, a monolayer metal gasket is disclosed, wherein the core plate around the bore apertures is made minimum in its own radial width at areas neighboring tightening holes formed in the perimetral member.
In the monolayer metal gasket of the present invention constructed as described just above, the minute variations in sealing stress occurring around the bore apertures may be properly, easily compensated or regulated with only changing partly the radial width of the core plate circumferentially of the bore aperture, without requiring altering partly the height of the bead raised on the core plate, whereby the sealing stress may be kept uniform throughout around every bore aperture. Thus, the monolayer metal gasket of the present invention is simple in construction and advantageous to easy regulation of the sealing stress, especially, when applied to the closed-deck type engine in which the water jackets are provided in an intermittent manner around the cylinder bores. Even if the areas neighboring the tightening holes experienced a considerably high tightening force, the sealing stress distribution would be kept uniform throughout around every bore aperture by means of the core plate varied in radial width circumferentially of the bore apertures, thereby helping ensure the improvement in sealing performance.